Glucose sensors of the type employing enzymes are well known. Many of these feature an "enzyme electrode" which consists of an immobilized enzyme such as glucose oxidase that catalyzes a chemical reaction involving glucose and oxygen--a reaction that involves the catalytic conversion of glucose to gluconic acid with simultaneous consumption of oxygen. The resulting decrease in oxygen may be measured by a current sensitive oxygen electrode.
Various arrangements for glucose sensors are described in the following U.S. Pats: U.S. Pat. No. 4,703,756 which utilizes first and second tandem sensor elements mounted in a catheter, one of which sensors acts as a reference and the other of which contacts glucose oxidase, whereby an electrical signal is produced indicative of the oxygen content differential between the two sensors; U.S. Pat. No. 4,240,438 which uses a hydrophobic membrane on which the glucose oxidase is immobilized and which senses the rate of oxygen consumption by the glucose contained in the blood; U.S. Pat. No. 4,655,880 which provides a multiple electrode sensor for measurement of glucose concentration by comparing electron current flow in working and counter electrodes in relation to current flow in a reference electrode; U.S. Pat. No. 3,979,274 which utilizes a laminated enzyme electrode with special filtering properties thereby eliminating the need for a compensating or reference electrode; U.S. Pat. No. 4,224,125 which has an enzyme electrode using an oxidoreductase and a redox copolymer acting as an electron mediator in an enzymatic reaction maintained in an immobilized state on an electron collector or semi-permeable membrane; U.S. Pat. No. 4,376,689 wherein the coenzyme is immobilized directly on an electron collector [eliminating the need for a membrane] whereby the activity of the enzyme on a substrate can be directly measured; U.S. Pat. No. 4,418,148 employing a contiguous multilayer membrane structure enabling a more homogeneous distribution of enzyme.
At present there does not exist an enzyme type glucose sensor providing the advantage especially for use in vivo [i.e., implantable] whereby the spent enzyme material may be replaced transcutaneously.